The present invention is a communication method and apparatus for locating tags in a communication region and particularly for locating tags using a combination of radio and acoustic frequencies to provide range and direction from a reference location to one or more locations. The present invention is particularly useful where large numbers of tags are present in the communication region, where the locations or identities of the tags in the communication region are not necessarily known, where transport of the tags to and from the communication region is not necessarily restricted and where contentions among communications to and from tags need to be resolved in a time and energy efficient manner.
Tags can be attached to items such as parts, equipment, furniture, vehicles or to persons, to livestock or to any object having requirements to be located. Examples of processes using tag location are manufacturing, warehousing, inventory management, storage and transfer facilities and personal communication systems.
The communication region in which the communication occurs to locate tagged items may be small or large, cellular or single celled or may have other characteristics. For example, in some applications, items may be in widely separated locations in a warehouse or may be grouped closely together in a small storage container. Also, tags may be attached to compound items having components where each component is itself a tagged item. Examples of such compound items are manifests, bills of lading, manufacturing travelers, transport trailers, containers or similar elements.
A common requirement of manufacturing, transportation, repair, warehousing or merchandising enterprises is to locate and keep track of items. Normally this requirement necessitates both a location system that provides knowledge of the existence of items and a method to physically locate items for retrieval or inspection. While maintaining knowledge of the existence of items is often burdensome, locating an item for retrieval or inspection is frequently even more burdensome. Often, items which are known to be in a building (or other communication region) cannot be found without arduous searching. For example, a storage container that is at one location at one time is often not at that same location at another time. At times, items seem to vanish from an original location, all searching to no avail, only to turn up at a later time at another location that may be only a short distance from that original location or may be a long distance from the original location. These occurrences are typical of large or unstructured storage lots or warehouses.
Many location systems require an accurate inventory list together with a reference map, diagram or other location information associated with the inventory list. Manually created maps or diagrams have been used to keep track of items, however, where there is frequent movement of the items, the necessity of updating of maps or diagrams to maintain current location data becomes a burden and the cost of record keeping may become excessive.
Automated means of updating inventory lists and location diagrams have been proposed to address the record keeping costs, where for example:
(1) optical bar code readers in warehouses and supermarkets monitor and track inventory in generalized areas; PA1 (2) magnetic stripe cards track the movement of persons at public transportation control points; and PA1 (3) radio frequency tags monitor tagged goods through electronic portals at retail establishments.
All of these examples utilize information to maintain location diagrams current, however, they implement the location process in what can be considered the reverse order. That is, the order is first to locate the item and then to record the present location of the item into the system. If the item cannot be located, then it is either presumed missing or a more extensive search is undertaken. With adequate time and a static warehouse (where items are not frequently moved), repeated searching will eventually ascertain the location of missing items. However, in many situations, there is not sufficient time to make a diagram or map, for example, in a shipping area where items are staged before forwarding, or in a deployment area where items that are brought in and stored at one time must be located and shipped at a subsequent time. In situations where items must quickly be located and retrieved, the search time required to locate items is frequently excessively long. Manual, diagram or map methods, as applied to item location and retrieval, are therefore inherently limited to structured, relatively stable storage environments so that search time is minimized.
In general, retrieving an item often requires both the knowledge of the location of the item relative to a reference location and directions as to how to proceed from the reference location to the location of the item. If vertical stacking is used, the directions should also include the level or height where the item may be found. An inventory list showing that the item exists is often not sufficient to locate the item, particularly if the item is in a large warehouse or storage yard. Although diagrams, maps or similar information indicating item locations may be useful, such information is frequently unavailable or not current.
Therefore, there is need for a method of locating items in regions without any pre-existing information as to the items's location other than, perhaps, the knowledge that the item is present in the region. A further desired feature of the location method is the ability to locate an item knowing only its serial number or other unique item identification. Such a method is needed to provide inventory status, location and other information.
Systems providing location information in unstructured situations where there is neither the time nor the resources to create and maintain location diagrams have been proposed. For example, radio direction systems designed to provide direction information are frequently used to determine location. Such radio direction systems employ antennas having field patterns that provide a high degree of signal amplitude resolution relative to antenna direction. These radio direction systems, however, are not practical in reflective (multipath) signal environments such as occur in or around buildings or in close proximity to the ground. In such environments, differentiating between the direct (unreflected) and indirect (reflected) multi-path radio signals is difficult since transit time differences between direct and multipath radio waves is on the order of one nanosecond per foot of path difference. The task of resolving the multipath signals is made even more difficult when the distance between the locating equipment and the object being sought is short (on the order of one hundred feet or less).
Procedures and equipment have been developed for use where multipath radio waves exist. In general, such equipment operates to analyze the combined radio signals and to statistically select the desired path from the reflected path. However, the methods employed are applicable generally only in long range situations or where the necessary computational time and resources are available and are cost-effective. For many applications, however, it is not practical to resolve by radio means the multipath signals typically found in a warehouse or storage yard.
Radio systems which employ multiple locators to provide triangulation information for item location are also limited in accuracy due to multipath effects. Additionally, proposed systems have been limited to the horizontal plane.
Even where the multipath problem is overcome, location systems still have not performed well because the penetrating characteristics of radio waves prevent formulation of practical directions from the reference location to the item location. If the item is behind a wall or other barrier, a radio system indicates a path through the barrier rather than an open pathway around the barrier.
The ideal locating system is one which gives practical instructions about a traversable path from the reference location to the item location. Often this traversable path is not a traversable direct line-of-sight path to the item location but rather the shortest unobstructed path to the item. This desired traversable path, the travel-path, is comprised of a travel-bearing and a travel-range.
Travel-range is the shortest unobstructed distance that the user of the locating system needs to travel to the item. Travel-bearing is the direction in which the user needs to travel from the instant position to most effectively reduce the remaining travel-range. These definitions are applied to the common situation wherein the observer is located in an obstructed environment such as an office suite with interior walls and doorways or a warehouse with product stacked or shelved in the surrounding area. If the desired item is located on the other side of an intervening wall or behind a row of stacked merchandise, it is preferable that the locating system not instruct the user to travel through the walls or the shelf structure but rather through one or more open doorways or aisles.
What is needed is a locating system that gives the user practical instructions as to travel-range and travel-bearing that the user needs to travel to reach the desired item, that is, to give the user the travel-path to the item. Additionally, the system should direct the user to the level or height where the item may be found when storage involves vertical stacking or shelving. The locating system must also reject multipath reflections which report ambiguous direction and must also be usable in all environments.
Prior art locating systems are not fully satisfactory. Prior art locating systems are concerned with either determining the distance to an object from a reference location or determining the instant location of a moving object with respect to a plurality of fixed references.
The Leyden patent (U.S. Pat. No. 3,566,348) discloses a ranging method using infrared and acoustic means to determine the distance from an observer to a spontaneous release of energy, specifically an explosion. The device uses an infrared sensor to detect the explosive release of energy, such detection initializing a counter. When the sound of the explosion reaches the device, the counter is stopped and the distance computed based on the time difference and the speed of sound. The direction is evident in this situation.
The Jones patent (U.S. Pat. No. 4,136,794) and the Kobayashi patent (U.S. Pat. No. 4,751,689) both disclose an acoustic ranging system (embodied as an apparatus to determine the distance to a pole located at a golf hole). The player uses an instrument to send a radio signal to the pole which then sends an acoustic signal back to the player. The time travel of the acoustic signal provides the information needed to compute the distance from the player to the pole. These methods provide useful information only if there is a direct line of sight to the pole as they do not afford any information as to the direction of the pole. In the Jones patent, misdirection of the signal from the player either gives distance to the wrong pole or does not give a distance reading. Kobayashi overcomes this limitation by sending a pole address as part of the radio signal. However, in either case, if the pole not within sight, direction is not evident.
The Hunt patent (U.S. Pat. No. 3,731,273) and the Schorum patent (U.S. Pat. No. 5,054,005) both teach methods of determining the location of a mobile station by generating a radio signal and energizing a spark gap at the mobile position. A plurality of fixed stations receive the signals, each determining the time difference at it's unique location of arrival between the energy from the spark and the radio wave. This art is concerned only with the position of the mobile station with respect to the fixed receivers.
The Edwards patent (U.S. Pat. No. 5,142,506) teaches the use of unique signatured acoustic waves to determine the ordinal coordinate system position of a mobile transmitter with respect to fixed receivers. This art is directed to the location of pointing instruments for use in plotting equipment.
The De Bruyne patent (U.S. Pat. No. 4,758,691) presents an apparatus for determining the position of a movable object with respect to two fixed acoustic sources. This patent is concerned with the accurate position determination of a computer accessory with respect to fixed references, the device to be used in controlling the cursor on a computer screen.
None of the prior art address or demonstrate methods or apparatus capable of determining the beating of a target item from a reference location nor do they teach methods of determining the path (that is, range, bearing and height) to an item.